[efi-boot-shim.git] / README.md

# shim, a first-stage UEFI bootloader

shim is a trivial EFI application that, when run, attempts to open and
execute another application. It will initially attempt to do this via the
standard EFI `LoadImage()` and `StartImage()` calls. If these fail (because Secure
Boot is enabled and the binary is not signed with an appropriate key, for
instance) it will then validate the binary against a built-in certificate. If
this succeeds and if the binary or signing key are not forbidden then shim
will relocate and execute the binary.

shim will also install a protocol which permits the second-stage bootloader
to perform similar binary validation. This protocol has a GUID as described
in the shim.h header file and provides a single entry point. On 64-bit systems
this entry point expects to be called with SysV ABI rather than MSABI, so calls
to it should not be wrapped.

On systems with a TPM chip enabled and supported by the system firmware,
shim will extend various PCRs with the digests of the targets it is
loading.  A full list is in the file [README.tpm](README.tpm) .

To use shim, simply place a DER-encoded public certificate in a file such as
pub.cer and build with `make VENDOR_CERT_FILE=pub.cer`.

There are a couple of build options, and a couple of ways to customize the
build, described in [BUILDING](BUILDING).
Commit	Line	Data
2616b136 CW	1	# shim, a first-stage UEFI bootloader
2616b136 CW	2
3df9e294 MG	3	shim is a trivial EFI application that, when run, attempts to open and
3df9e294 MG	4	execute another application. It will initially attempt to do this via the
2616b136 CW	5	standard EFI `LoadImage()` and `StartImage()` calls. If these fail (because Secure
2616b136 CW	6	Boot is enabled and the binary is not signed with an appropriate key, for
3df9e294	7	instance) it will then validate the binary against a built-in certificate. If
25c83246	8	this succeeds and if the binary or signing key are not forbidden then shim
3df9e294 MG	9	will relocate and execute the binary.
	10
	11	shim will also install a protocol which permits the second-stage bootloader
	12	to perform similar binary validation. This protocol has a GUID as described
	13	in the shim.h header file and provides a single entry point. On 64-bit systems
9a960c6e PM	14	this entry point expects to be called with SysV ABI rather than MSABI, so calls
9a960c6e PM	15	to it should not be wrapped.
3df9e294	16
631265b7 PJ	17	On systems with a TPM chip enabled and supported by the system firmware,
631265b7 PJ	18	shim will extend various PCRs with the digests of the targets it is
2616b136	19	loading. A full list is in the file [README.tpm](README.tpm) .
631265b7	20
81ee561d	21	To use shim, simply place a DER-encoded public certificate in a file such as
2616b136	22	pub.cer and build with `make VENDOR_CERT_FILE=pub.cer`.
1e717349 PJ	23
1e717349 PJ	24	There are a couple of build options, and a couple of ways to customize the
2616b136	25	build, described in [BUILDING](BUILDING).